In recent years, the use of cellular communication networks or systems having mobile devices which communicate with a hardwired network, such as a local area network (LAN) or a wide area network (WAN), has become widespread. The mobile devices, commonly referred to as mobile terminals, may take one of several different forms. For instance, in retail stores hand-held scanning units may be used to allow for scanning inventory bar codes. In a warehouse, portable units mounted to a vehicle may be used to gather information from the warehouse floor. In a medical environment, the mobile terminal may take the form of a pen based workslate which allows medical personnel to work with full page screens at once.
In a typical cellular communication network, each mobile terminal communicates with a networked system via a radio link in order to allow for a real time exchange of information. The mobile terminals communicate through one of several base stations interconnected to the network. The base stations allow for a wireless data communication path to be formed.
Each mobile terminal and base station communicate via their respective transmitter and receiver (i.e., transceiver) systems. Typically, the transmitter and receiver in each device share the same antenna and a control signal is used to switch the antenna between a transmitting and receiving mode.
Due to various local and/or federal regulations relating to the use of cellular communication devices such as mobile terminals and base stations, these devices are designed to transmit information at or below a predetermined power level. For example, telecommunication standards adopted by the Federal Communication Commission (FCC) in the United States of America requires that cellular communication devices not exceed a predetermined maximum output power level when transmitting information. Various international telecommunication standards such as the ETSI in Europe and MKK in Japan also have adopted similar requirements. Consequently, manufacturers of cellular communication devices may, at least in theory, set the output power level at approximately the maximum allowed output power level.
Unfortunately, due to several factors including temperature swings, component selection and tolerances, wear, frequency variations, etc., the actual output power can vary substantially. For instance, in the United States a 20 decibel/milliwatt (dBm) rated output power level for a mobile terminal or base station can vary by as much as 3 dB simply due to changing temperature conditions alone. Given the limitations set by the FCC, manufacturers are therefore forced to reduce their rated output power level from the maximum allowable by the FCC in order to avoid situations where the output power drifts above the permitted maximum due to one or more of the factors mentioned above. This, in turn, significantly reduces the maximum obtainable range of each of the devices.
In order to better maintain a constant output power level, automatic gain control (AGC) loops have been used in radio transmitters. AGC uses an analog circuit to compare an output power level with a reference power level and adjust the gain according to the difference at any given time. Unfortunately, AGC loops are quite complicated to construct and manufacture due to the need for precise analog components and are typically only useful in linear gain type systems.
Furthermore, the power needed by a mobile terminal to carry out the wireless communications described above typically is supplied from a rechargeable battery included in the mobile terminal. Rechargeable batteries composed of Ni-Cad, Li-Ion or Ni-metal-Hydride are often used. Therefore, in addition to the desire to transmit information at the maximum allowable power level, battery life conservation is also of significant concern in order to extend the working life of the mobile terminal prior to needing recharging.
In view of the aforementioned shortcomings associated with existing cellular communication devices, there is a strong need in the art for a method and system for automatically controlling the output power of such devices. There is a strong need for such a device which allows the output power level to be maintained at or near the maximum output power level allowed by the relevant regulating body. Further, there is a strong need for such a device which can also conserve battery life when certain operating conditions are met.